Modified phenolic tackifier

ABSTRACT

Tack is imparted to uncure elastomers by the inclusion of the product of the reaction between an alkylphenol-formaldehyde condensation product having methylol groups with di-2-hydroxyalkylamine or morpholine. In addition to imparting tack to the elastomer, the tackifier of this invention does not interfere with but tends to enhance the development of adhesion of the elastomer to reinforcing fibers.

This is a division of application Ser. No. 669,434 filed Mar. 22, 1976,now abandoned.

BACKGROUND OF THE INVENTION

During the fabrication of rubber articles, it is common for unvulcanizedcalendered sheets to be laminated to obtain the desired structuralconfiguration. This technique of building up of layers of uncuredelastomer is used extensively in the tire building industry, but alsofinds utility in the manufacture of other rubber articles such asmechanical goods and hoses. In order that the unvulcanized compositeshave the necessary mechanical stability toward handling and storage, theelastomeric materials must have sufficient tack so that the desiredconfiguration is retained through the vulcanization step. This tack isthe ability of unvulcanized elastomer to adhere to itself or to anotherelastomer which also has tack. This adhesive property, known as"building tack" plays an important role in the production of rubbergoods. In the manufacture of tires, "building tack" holds theinnerliner, beads, plys, sidewalls and tread together prior tovulcanization.

Natural rubber has the advantage of having sufficient tack withouttackifying resins being added. However, synthetic rubbers lack thisbuilding tack, and the use of resinous modifiers is necessary to obtainthe tack required for fabrication. It is not uncommon, however, to addtackifiers to natural rubber or to blends of natural and syntheticcompounds to aid in tack retention during storage of calenderedunvulcanized stock. Tackifiers also provide secondary benefits byreducing compound viscosity and also by functioning as plasticisers.

A number of different types of materials are utilized as rubbertackifiers. These include various hydrocarbon resins made fromfeedstocks derived principally from petroleum cracking and coal taroperations. Aliphatic and aromatic type hydrocarbon resins are producedprimarily from petroleum derived streams. While coumarone-indene resinsare coal tar derived, similar resins are also made from petroleumsources. Polyterpenes, terpene phenolics, rosin and rosin derivatives,alkylphenol-aldehyde resins, alkylphenol acetylene resins, naturalrubber and reclaimed rubber are also utilized as rubber tackifiers.

The hydrocarbon resins are in general less expensive than are thephenolics, but require the use of up to three times the amount to giveequivalent tack with tack retention being adversely affected. Sincetackifiers which remain in the fabricated rubber article can tend todetract from the properties of the rubber, phenolics are oftenadvantageously used because of the lower level required. However,phenolic tackifiers do tend to decrease the adhesion of the rubber towire or other reinforcing fibers. For this reason, hydrocarbon resinsare sometimes used, even though higher percentages are required, whenadhesion of the rubber to reinforcing materials is critical. Thisinvention provides phenolic tackifiers having desirable efficiency withno adverse effect on the adhesion of the rubber to the reinforcingelement.

SUMMARY OF THE INVENTION

This invention concerns a tackifier for unvulcanized elastomerscomprising an alkylphenol-formaldehyde condensation product havingaminomethylene groups on the phenolic ring. These compounds are preparedby the reaction of the corresponding alkylphenol-formaldehyde resincontaining terminal methylol groups with di-2-hydroxyalkylamine ormorpholine, or by the reaction of an alkylphenol-formaldehyde novolacwith di-2-hydoxyalkylamine or morpholine in the presence offormaldehyde, or by the reaction of an alkylphenol with formaldehyde andmorpholine or di-2-hydroxyalkylamine.

These compounds can also be prepared by the reaction of thecorresponding alkylphenol-formaldehyde product with aN-methylol-dialkanol amine.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Phenol-formaldehyde resins normally used for imparting tack toelastomers are of the oil soluble, non-heat reactive type, prepared bythe acid catalyzed reaction of a para-substituted alkyl phenol withformaldehyde. The structure of such a polymer is believed to approximatethat shown in FIG. I. ##STR1##

The compatability of the resin is dramatically affected by the molecularweight (value of X) and by the R group in the para-position. Thesenonreactive polymers remain relatively unchanged at vulcanizationtemperatures.

Heat reactive alkylphenol-formaldehyde resins, on the other hand, tendto polymerize further and can lead to agglomerations of brittlethermoset polymers, resulting in a stiffening of the rubber withaccompanying disadvantageous effect on modulus and tensile strength.These heat reactive polymers have structures approximately shown in FIG.II. ##STR2## We have found that the polymers of FIG. II, or the polymersof FIG. I when heated with additional formaldehyde to form terminalmethylol groups, can be converted to aminomethylene derivatives byreaction with either morpholine or di-2-hydroxyalkylamines. FIG. IIIshows the reaction sequence starting with the alkylphenolic polymer ofFIG. I. FIG. IV shows the reaction sequence starting with thealkylphenolic polymer of FIG. II. The reaction of primary and secondaryamines with formaldehyde and active hydrogen compounds (the Mannichreaction) has been widely studied (Organic Reactions, Wiley, Vol. 1,Chap. 10, p. 303). This invention is concerned with the Mannich reactiononly as it applies to phenols, (specifically to p-alkyl phenols) andmorpholine or di-2-hydroxyalkylamines. U.S. Pat. Nos. 2,040,039 and2,040,040 disclose the ease of the condensation of alkylated phenol,formaldehyde and morpholine to form the correspondingmorpholinomethylenephenols. U.S. Pat. No. 3,001,999 discloses thereaction of p-alkylphenol with formaldehyde and amines, includingmorpholine. U.S. Pat. Nos. 3,173,952 and 2,997,455 disclose theaminoalkylation of dialkylphenols; German Pat. No. 2,320,526 disclosesaminoalkylation using diethanolamine.

We have found that aminomethylene terminated alkylphenols and polymersthereof, when the amine group is morpholine or a diethanolamine, willimpart good tack properties to uncured rubber and, most important,provide good tack retention and also not diminish, and will usuallyenhance, the adhesion of the rubber to the reinforcing elements.

Tackifiers employed according to the present invention when the aminegroup is a dialkanol amine can be represented by the formula: ##STR3##where

R is alkyl

R¹ is CHR³ -- N -- (CH₃ --CHOHR³)₂ wherein R³ is alkyl or hydrogen,

R² is R¹ or a mixture of R¹ with H or - CHR³ OH, or both, provided thatwhen R² is a mixture, R¹ is the predominant constituent of the mixture,

and where m plus n is at least 1.

The phenolic component for the compounds of this invention is adifunctional hydroxybenzene, having an alkyl substituent in the paraposition which contains 1-24 carbon atoms, preferably 4-12 carbon atoms.Phenols with additional substituents in the meta position are operable,but are not preferred. The alkylation procedure used to prepare thealkyl phenols is usually carried out under acid catalysts withequimolecular amounts of phenol and the alkylating agent, but normally aportion (2-5%) of the alkylation takes place in the ortho positionwithout deleterious effect on the performance of the tackifier. Thepresence of a small amount of dialkylphenol, obtained by use of greaterthan stoichiometric amount of alkylating agent, has been found in somecases to lead to higher adhesion and tack values than expected. Typicalalkylating agents are diisobutylene (octylphenol) tripopylene(nonylphenol) and tetrapropylene (dedecylphenol). The amines used toprepare the tackifier resin of this invention are morpholine and amineswhich can be dehydrated to morpholine, such as diethanolamine anddi-2-hydroxy propylamine.

The molar ratio alkylphenol formaldehyde/amine can vary widely. At oneend of the spectrum would be 2,6-diaminomethylene-4-alkylphenol with amolar ratio of 1/2/2. At the other extreme would be a ratio ofalkylphenol/formaldehyde/amine of 20/28/2. The ratio selected depends,among other factors, on (1) the physical properties of the resin whichare desired for easiest handling of the resin and the tackified rubber(2) the melting point desired and (3) the cost limitations. Thus,although fluid compositions are effective, we have found that preferredtackifiers have softening points between 85° and 135° C., and mostpreferably between 95° and 120° C. The reaction conditions for thephenol-formaldehyde condensation will also affect the ratio, since basicconditions will tend to increase the amount of benzylic ether linkages,thus increasing the formaldehyde required. This invention includes allthese p-alkylphenol-formaldehyde condensation products having terminalmorpholinomethylene groups, when such materials are used to improve tackof uncured rubber and to maintain the adhesive strength of therubber-reinforced fiber bond. A typical rubber composition employing atackifying compound of the type used according to the present inventionincludes brass coated steel, polyester or poly aromatic amidereinforcing fibers and the vulcanization product of uncured natural orsynthetic rubber or their mixtures, extender oil, carbon black, curativeagents and from 2 - 5 parts per hundred parts of rubber of a tackifyingcompound of the type employed according to the present invention.

Table I shows the various resins prepared and evaluated. Examples 1through 4 are standard types of tackifiers commercially available.Examples 5-7 have been modified with polyamines, giving resins whichhave not shown significant improvement in adhesion, and are deleteriousto tack retention. Examples 8-14 show the preparation of compounds ofthis invention, based on morpholine and diethanolamine. The proceduresA-E listed in Table I are as follows:

Procedure A.

The phenolic component and formaldehyde (50% aqueous) and acid catalystwere charged simultaneously to a reaction vessel and reacted at 100° C.After the prescribed reaction time, the product was vacuum dehydrated tothe desired softening point.

Procedure B.

The phenolic component, acid catalyst and azeotroping solvent wereheated at least to the boiling point of the solvent, and aqueousformaldehyde was added incrementally while continually azeotropicallyremoving water. Solvent was removed by vacuum distillation when thecondensation was complete.

Procedure C.

The phenolic component in an azeotroping solvent was heated until thephenolic component dissolved. The amine component was added slowly sothat the exotherm of dissolution did not cause the temperature to exceed130° C. In these cases (Examples 8-11, 13, 14) where the amine wasmorpholine, 2-10% of triethylamine (TEA) catalyst (based on morpholineand phenol) was used. The formaldehyde (50% aqueous) was then addedeither as one charge (Examples 1, 3, 8, 10, 13, 14) or intermittantly(Examples 2, 5, 7, 11, 12, 15. When added as one charge, the reactionwas run at full reflux, and the solvent and water were removed at thecompletion of the reaction by vacuum distillation. When addedincrementally, the water was continually removed azeotropically over thetime of formaldehyde addition.

Procedure D

Resin of Example 2 (octyl phenol novolac) was dissolved in sufficienttoluene to make an 80% solids solution, heated to 110° C., and thesecondary amine was added in one charge (TEA catalyst was added whenmorpholine was used). The temperature was raised to 120° C., andformaldehyde was added incrementally while continually azeotroping thewater. The solvent was then removed by vacuum distillation.

Procedure E

Dimethylol octylphenol was prepared by the base (lithium hydroxide 93%and TEA 4%) catalyzed condensation of octylphenol (1 mole) with 50%aqueous formaldehyde (2 moles). The dimethyloctylphenol product wasdissolved in toluene/benzene at 65% solids. Morpholine was added in onecharge, and the reaction mass was refluxed to completion and vacumndehydrated to the desired softening point and methylol content of lessthan 1%. This value for methylol content includes methylol groups andbenzylic ether bridges.

                                      Table I                                     __________________________________________________________________________                    Overall        Time                                                           Mole Ratio     for  Catalyst                                                  phenolic/CH.sub.2 O/                                                                         CH.sub.2 O                                                                         Level                                                                              Softening                            Example                                                                            Procedure                                                                           R.sup.8                                                                            amine    Amine Addition                                                                           TEA  Point.sup.9                          __________________________________________________________________________    1.   A     octyl.sup.1                                                                        1/0.9/0  --    --        85°-105° C.            2.   B     octyl                                                                              1/0.95/0 --    4 hrs.    110°-130° C.           3.   B     dodecyl.sup.2                                                                      1/1.25/0 --    5 hrs.    95°-115° C.            4.   Resin of Example 1 plus 25% pentaerythritol ester of rosin acids         5.   C     t-butyl                                                                            1/1.15/0.25                                                                            TETA.sup.4                                                                          3 hrs.    113.5° C.                     6.   C     nonyl                                                                              1/1.35/0.25                                                                            TETA  3 hrs.    106° C.                       7.   C     t-butyl.sup.3                                                                      1/2.3/0.5                                                                              EDA.sup.5                                                                           3 hrs.    99° C.                        8.   C     H    1/3.5/1  Morpholine                                                                          --   5%   96° C.                        9.   C     t-butyl                                                                            1/3.2/1  Morpholine                                                                          --   10%  paste                                10.  C     octyl.sup.6                                                                        1/2.3/1.1                                                                              Morpholine                                                                          --   9%   liquid                               11.  D     octyl                                                                              1/1.2/0.23                                                                             Morpholine                                                                           20 min.                                                                           3%   104° C.                       12.  D     octyl                                                                              1/1.2/0.23                                                                             DEA.sup.7                                                                            25 min.                                                                           --   151° C.                       13.  E     octyl                                                                              1/2/0.66 Morpholine                                                                          --   4    93° C.                        14.  E     octyl.sup.6                                                                        1/1.7/0.67                                                                             Morpholine                                                                          --   4    82° C.                        15.  C     octyl                                                                              1/2/2    Morpholine                                                                          100 min.                                                                           4%   liquid                               __________________________________________________________________________     .sup.1 From the alkylation of phenol with                                     .sup.2 From the alkylation of phenol with                                     .sup.3 From the alkylation of phenol with                                     .sup.4 Triethylene tetramine                                                  .sup.5 Ethylenediamine                                                        .sup.6 The phenolic was prepared by alkylation of phenol with                 diisobutylene at a molar ratio of olefin to phenol of 1.5/1. Therefore,       some of the active positions have been substituted with alkyl groups.         .sup.7 diethanolamine                                                         .sup.8 R is the para alkyl group on the                                       .sup.9 ASTM Ring and Ball Softening Point E 28-67                        

The recipe for the rubber stock used in these evaluations was asfollows:

#1RSS - 40 parts -- #1 Ribbed smoked sheets, a grade of natural rubber(described in Vanderbilt's Rubber Handbook, 1968 Edition) which must bedry, clean, free from blemishes, resinous material, sand, dirty packingor other foreign material. Ribbed smoked sheets comprise coagulatedrubber sheets properly dried and smoked and cannot contain cuttings,scrap, frothy sheets, weak, heated, or burnt sheets. Air dried or smoothsheets are not permissable.

SBR 1502 - 40 parts -- A standard styrene-butadiene rubber containing23.5% bound styrene and nominal Mooney Viscosity (ML 1 + 4) at 212° F.of 52. It is non-staining and is prepared using fatty acid-rosin acidtype emulsifier and is a standard, cold-polymerized, non-pigmented SBR.

Cis -1,4 - Polybutadiene - 20 parts -- Butadiene homopolymer of high Cis-1,4-content. Budene 501, (Goodyear) is a non-staining, solutionpolymerized gum with Mooney Viscosity (ML 1 + 4) at 212° F. of 45-55.Cis content is approximately 93%.

N 660 - 45 parts per hundred resin (PHR) - GPF (General Purpose Furnace)-- A carcass grade carbon black with particle diameter about 62nanometers, DPB absorption .91 cm³ /g., ASTM iodine No. 36, and bulkdensity 26 lb/ft³.

Circo Light 9 PHR - RPO (Rubber Process Oil) -- Similar to ASTM #3 oil,a napthenic type oil with SUS viscosity 156 at 100° F., specific gravity0.922 at 60° F., mol. wt. about 330, and anilene point 157° F. Viscosityindex intermediate between paraffinic and aromatic oils, manufactured bySun Oil Co.

Santoflex 13 - 1.9 PHR -- An antiozonant manufactured by Monsanto.

Insoluble Sulfur 60 - 2.75 PHR -- Vulcanizing agent manufactured byMonsanto.

Santocure - 0.9 PHR -- Delayed action accelerator; Monsanto

Santogard PVI - 0.25 PHR -- Pre-vulcanization Inhibitor; Mansanto

Tackifier 3 PHR -- The control in Tables II-IV does not contain anytackifier resin.

Rubber Compounding -- The rubber compound was made in two steps. Stepone involved mixing all ingredients except the curatives (sulfur,Santocure and Santogard PVI) in a Banbury mixer for a total of 5-6minutes at 330° F. The curatives were added in step 2 and the mass wasmixed for an additional 2-3 minutes at 220° F.

Tack Test -- The rubber compound was milled to a thickness of 60 mil,and placed on Holland cloth. The exposed side was covered with polyesterfabric. The composite was pressed at 200° F. and 75 psi for 2 minutes toremove surface irregularities and to force the polyester reinforcementinto the rubber stock. Two 0.75 × 2.0 inch strips were stripped of theHolland cloth, and pressed together. The tack was determined using aMonsanto Tel-tak instrument with a 30 second dwell time and a 16 oz.weight on the sample. Additional samples were held for 72 hours at highhumidity, and the tack of these humid-aged samples was determined. Thetack values shown in Table II include tack and also the percent tackretention after humid aging (i.e. Example 1 shows 37.5 ± psi atseparation with 120% tack retention after humid aging). The separateseries I-V are individual testing programs, and the values should becompared with the value for the control (rubber compound withouttackifier) in each series.

                  Table II                                                        ______________________________________                                        Tack Evaluation.sup.1                                                         Example #            Control          Series                                  ______________________________________                                        1        37.5±1.6/120                                                                           36 1/63                                                  4        35.2±1.4/114                                                                           "                I                                       2        36.9±1.8/120                                                                           "                                                        3        37.5±1/106                                                                             "                                                        8        39±2.1/47                                                                              39.6±2.2/36                                                                                 II                                      9        37.6±1.6/48                                                                            "                                                        1        40.7±2.3/82                                                                            39.1±2.5/73                                           10       39±1/89  "                III                                     11       36.5±2.1/88                                                                            "                                                        12       38±1/69  "                                                        1        27.4±1.5/105                                                                           30.7±1.5/59                                           13       27.1±1.2/103                                                                           "                IV                                      14       23.2±1.5/112                                                                           "                                                        1        30±5 1.8/106                                                                           28.4±1/25                                             10       27±1.8/53                                                                              "                V                                       11       28.5±1.1/107                                                                           "                                                        ______________________________________                                         Humid aging conditions for determining tack retention                         Series I - 72 hrs. at 80° F. and 70% RH                                Series II - 72 hrs. at 80° F. and 70 % RH                              Series III - 72 hrs. at 70° F. and 50% RH                              Series IV - 72 hrs. at 70° F. and 50% RH                               Series V - 72 hrs. at 85° F. 90-95% RH                            

Static Adhesion -- Table III shows the data obtained by testing theruber stock without tackifier (Control) and with the various tackifyingresins, according to ASTM D 2229-73, Adhesion of Vulcanized Rubber toSteel Cord. The steel cord used was National Standard 6-3 wire (brasscoated steel). Cure time was T_(o) ¹ (90)+ six minutes mold fctor time.Embedment length of wire in the block was 0.75 inches. Table III givesthe values, for series I-VI, for both adhesion and coverage (i.e.Example 1, 31±7 pounds required to extract wire, with 10% coverage).Coverage was determined by visual examination by the pulled wire.

                  Table III                                                       ______________________________________                                        Static Adhesion Evaluation                                                    (ASTM2229)                                                                    Example #            Control          Series                                  ______________________________________                                        1       31±7/10    93±11/80                                             5       26±5/<5   "                I                                       6       26±3/<5   "                                                        1       59.9±8.6/50                                                                             84.6±8.2/80                                           4       71.5±8.4/50                                                                             "                                                        2       50.9±10/50                                                                              "                II                                      3       50±7.6/30 "                                                        1       34±3.4/10 98.9±5.9/70                                           7       51.7±7.1/30                                                                             "                                                        8       118.1±14.8/90                                                                           126.5±14.1/90                                                                               III                                     9       145.9±15.1/90                                                                           "                                                        10      138.3±15.1/80                                                                           127.8±13.8/70                                         11      103±8.9/80                                                                              "                IV                                      12      103.2±7.4/80                                                                            "                                                        13      158.5±16/100                                                                            "                                                                                              V                                       14      142.3±7.4/100                                                                           "                                                        1       121.2±11.4/80                                                                           156.6±12.3/90                                         10      174.9±11.5/95                                                                           "                VI                                      11      183.6±12.4/100                                                                          "                                                        ______________________________________                                    

Table II shows conclusively that the compounds of this invention(Example 8-14) develop the same degree of tack as do conventional,commercially acceptable phenolic tackifiers (Examples 1-4).

Table III shows dramatically the surprising increase in static adhesionwhich is observed using the compounds of this invention when compared toconventional phenolic tackifiers. Examples 5-7, which are aminomethylenesubstituted phenolics using other than di 2-alkanolamines or morpholineas the amine do not give the superior results which are obtained by useof morpholine or di-2 hydroxyalkylamines.

What is claimed is:
 1. A method for improving tack and tack retention inuncured, vulcanizable elastomers while maintaining acceptable adhesionof the cured elastomer to reinforcing elements, comprising dispersing insaid elastomer a tackifying compound of the structure ##STR4## where Ris alkyl R¹ is ##STR5## where R³ is alkyl or hydrogen, R² is R¹ or amixture of R¹ with H or -- CHR³ OH, or both, provided that when R² is amixture, R¹ is the predominant constituent of the mixture,and where mplus n is at least
 1. 2. The method of claim 1 wherein R is an alkylgroup of 4 - 12 carbon atoms, and wherein R³ is hydrogen.
 3. The methodof claim 2 wherein R is octyl.
 4. The method of claim 3 wherein thetackifying compound has a softening point of between about 85° C. and130° C.
 5. The method of claim 3 wherein the tackifying compound has asoftening point of between about 95° and 120° C.
 6. The method of claim5 wherein the tackifying compound has a free methylol content of lessthan 2 weight percent.
 7. A method for improving tack in uncured,vulcanizable elastomers while maintaining acceptable adhesion of thecured elastomers to reinforcing fibers comprising dispersing in saidelastomers, a tackifying compound prepared by the reaction of ap-alkylphenol formaldehyde condensation product of the structure##STR6## where R is alkyl, R¹ is -- CHR³ OH,R² is R¹ or a mixture of R¹with H, R³ is H or lower alkyl, provided that when R² is a mixture, R¹is the predominant constituent of the mixture, and where m plus n is atleast 1, with di-2-hydroxyalkylamine.
 8. The method of claim 7 wherein Ris octyl and wherein the softening point of said tackifying compound isbetween 90° and 120°.
 9. The method of claim 8 wherein the tackifyingresin contains a ratio of said p-octylphenol to formaldehyde of from1-0.5 to 1-2.2, and a ratio of phenol to said di-2-hydroxyalkylamine offrom 1-0.1 to 1-2.0.
 10. A method for improving tack in uncured,vulcanizable elastomers while maintaining acceptable adhesion of thecured elastomer to reinforcing fibers comprising dispersing in saidelastomers a tackifying compound prepared by the reaction ofp-alkylphenol-formaldehyde condensation product of structure. ##STR7##where R is alkyl, R³ is H or lower alkyl,and where m plus n is at least1, with formaldehyde and di-2-hydroxyalkylamine.
 11. The method of claim10 wherein R is octyl, and where the softening point of said tackifyingcompound is between about 95° C. and 120° C.
 12. A method for improvingtack in uncured vulcanizable elastomers while maintaining acceptableadhesion of the cured elastomer to reinforcing fibers comprisingdispersing in said elastomers a tackifying conpound prepared by thereaction of a p-alkylphenol-formaldehyde condensation product of thestructure: ##STR8## where R is alkyl, R³ is H or lower alkyl with N -methyloldialkanol amine,and where m plus n is at least
 1. 13. Avulcanized rubber composition containing brass coated steel, polyesteror poly aromatic amide reinforcing fibers comprising the vulcanizationproduct of uncured natural or synthetic rubber or their mixtures,extender oil, carbon black, curative agents, and from 2-5 parts perhundred parts of rubber of a tackifying compound of the structure##STR9## where R is alkyl, R¹ is CHR³ - N - (CH₃ CHOHR³)₂,R³ is alkyl orhydrogen, R² is R¹ or a mixture of R¹ with H or CHR³ OH, or both,provided that when R² is a mixture, R¹ is the predominant constituent ofthe mixture, and where m plus n is at least
 1. 14. The composition ofclaim 13 wherein R is octyl and where R³ is hydrogen and where saidtackifying resin has a softening point of 95° C. to 120° C.
 15. Thecomposition of claim 13 wherein R is octyl and where R³ is hydrogen andwhere said tackifying resin is a liquid and has a viscosity at 35° C. ofup to 1200 poises.